The commercial printing of pictures from roll film is normally accomplished by transporting roll film under a light source while simultaneously transporting unexposed photosensitive paper through a photographic printing apparatus. The roll film is indexed through the printing apparatus and is stopped as each negative image registers with a window or aperture through which the light from the light source may be projected. Generally, a shutter and appropriate optics are located between the film and the paper. The shutter may be triggered automatically or manually, depending upon type or mode of operation of the printing apparatus.
In order to stop the film automatically as each exposed negative moves into registration with the exposure window some positive method of indexing must be used. One indexing method counts sprocket holes or perforations along the edge of the film; another utilizes punched holes located on one side of the negative, each hole associated with a negative image. In both the sprocket hole system and the punched hole system, a pin is normally inserted through the appropriate sprocket hole or punched hole in order to stop the film in proper registry.
Non-perforated film requires some other method for achieving registration of exposed negatives with an exposure window. U.S. Pat. No. 3,752,578, issued to Allen on Aug. 14, 1973, discloses a microfilm transport and enlarger, wherein the film transport motor is controlled to position an image relative to the optical axis of the enlarger. The Allen patent, in controlling the drive motor, suffers from two disadvantages; the first being a possible lack of accurate and positive registration between the negative and the optical axis; the second being the time delay inherent in stopping and starting the film drive as the motor is slowed, then stopped prior to exposure and then started after exposure.
Accordingly, this invention is a film strip controller for use on a commercially available photographic printing apparatus which has a conventional roll film transport employing slip clutches on the film transport drive and normally used for perforated film strips. The film strip controller is specifically for controlling non-perforated roll film.
In particular, this invention utilizes a circuit sensitive to light such as the light of the photographic printing apparatus to sense a mark resulting from exposure on an edge on a roll of photographic film in a specially configured camera such as disclosed in U.S. Pat. No. 3,810,218 as well as other marks existent along the same edge of a developed film for control purposes.